This invention relates generally to a pollution control and recovery method and apparatus, and specifically relates to a control and recovery method and apparatus which is continuous in nature and which utilizes magnetic phenomena.
As is well known to those skilled in the art, oil spills resulting from offshore accidents of large oil containing vessels and from offshore drilling operations have resulted in literally billions of dollars of damages world wide. More important than the monetary value of the damages, however, is the damage done to marine and shoreline eco-systems by such hydrocarbon pollutants. Even assuming that the billions of dollars in clean-up costs are expended to remove the hydrocarbon pollutant, by which term is meant hydrocarbon liquids which are insoluble or sparingly soluble in water, the virtual impossibility of complete removal of pollutant results in residual levels of contamination which may continue to damage marine animal and vegetable life forms for periods of months and perhaps years.
Since by far the worst ecological damage which is caused by hydrocarbon pollutant spills is realized at the shoreline, the most often used post-spill operation is the isolation of the hydrocarbon pollutant from the shoreline. Various prior art devices have been devised to form an impenetrable barrier to the spread of the spill, and in some cases to completely surround the spill site, such that the hydrocarbon pollutant is restricted in its motion to a relatively small area. Such devices depend for their functionality on the physical characteristics of the hydrocarbon pollutant and the aquatic media upon which it is borne, i.e. the fact that the hydrocarbon pollutant is immiscible with water and that the pollutant has a density less than that of water. Among such prior art devices are those disclosed in U.S. Pat. Nos. 3,494,132 to Logan; 3,503,512 and 3,503,214 to Destry et al; and 3,577,879 to Ducrocq.
Irrespective of whether such barrier-type devices as those disclosed above are utilized, the removal of the pollutant spill from the surface of the aquatic media on which it is carried is the desired result. Once again the two physical characteristics of the two-componant media, i.e. immiscibility and density differences, are utilized by various "skimmer" devices for the collection of the organic pollutant. Among such prior art devices are those disclosed in U.S. Pat. Nos. 2,778,500 to Fuller; 2,876,903 to Lee; 3,221,884 to Mueller; 3,314,540 to Lane; 3,358,838 to Kosar et al; 3,508,652 to Woolley; 3,534,858 to Harrington; 3,534,859 to Amero et al; 3,578,171 to Usher; and 3,756,414 to Crisafulli. Several of the skimmer devices disclosed in these references utilize a buoyant oil sump having a weir type opening which is carried at approximately the level of the aquatic media such that the pollutant will flow over the weir and be contained in the sump. Other of the skimmer devices utilize rolls or inclined belts or plates which are rotated through the pollutant layer, thereby picking up a film of the pollutant which adheres to the rotating device, which film is subsequently wiped from the device in such a way as to be deposited in a pollutant sump. As an alternative to wiping, suction may be utilized, as for instance with surface borne rollers, to collect the floating pollutant.
U.S. Pat. No. 3,494,862 to Horowitz discloses that oil which has been spilled, as for instance in a machine shop or on water, may be removed therefrom by treating the oil with a porous polystyrene in which the oil subsequently becomes absorbed. The separation of the oil-polystyrene mass is accomplished by heating to a two phase liquid system and decantation. In addition to the foregoing, U.S. Pat. No. 2,907,717 to Hann discloses the fact that oil-water emulsions may be broken by treating the emulsions in a settling zone with an unsoluble polyethylene or polystyrene material which is impregnated with an emulsion breaking agent. By fabricating the material such that its specific gravity is intermediate that of the water and the oil, the emulsion may be broken into a two phase system having a barrier layer of the plastic material, impregnated with the emulsion breaking agent, residing therebetween. Finally, hydrocarbon pollutant spills have been collected by a method in which the spill is first isolated from the surrounding aquatic media by the use of buoyant devices, scattering a buoyant oil-bonding substance, such as peat or slag on the surface of the spill in order to bond the pollutant, and subsequently collecting the oil-substance mass by mechanical means.
Until relatively recently, the development of magnetic separation devices utilized for the separation of magnetic solids from non-magnetic media, has proceeded along a parallel, but unrelated, course. Exemplary of such magnetic separation devices are those disclosed in U.S. Pat. Nos., 531,183 to Harris; 1,317,557 to Davis; 2,430,157 to Byrd, Jr.; 2,717,080 to Anderson; 2,954,122 to Colburn; and 3,136,720 to Baerman. Each of the devices disclosed and claimed in the referenced patents utilizes a magnetic source, either naturally occurring or electrically generated, in order to attract magnetically susceptible particles from a mixture of both susceptible and non-susceptible particles so as to remove the magnetically susceptible particles from the mixture.
Swiss Pat. No. 477,665 to Leo Theiler, Horw discloses the collection and recovery of a hydrocarbon pollutant spill which combines the use of an oil bonding substance with magnetic collection means. In order to accomplish the collection phase, the Theiler patent discloses the mixing of an oil-bonding material with particles of iron, i.e. powder or chips, in order to form a buoyant granular substance. As with peat or slag, the granular substance is subsequently scattered over the surface of the hydrocarbon pollutant in order that the pollutant may become bonded thereto. After a time sufficient for a bonding interaction to take place between hydrocarbon and bonder, the resultant pollutant mass is subjected to a magnetic field generated either electrically or through use of permanent magnets in order to attract the mass through the magnetically susceptible iron particles. By so doing the mass may be attracted to the magnet thereby collecting not only the iron containing bonding material but also the bound hydrocarbon pollutant. The Theiler patent discloses that, while peat and/or slag may be used as the oil bonding material, charcoal, such as wood charcoal or the like, is preferred due to the fact that such charcoal preferentially absorbs hydrocarbon liquids rather than water. Thus the Theiler sorbent is disclosed as comprising a mixture of iron particles and charcoal which are bound together by any suitable adhesive in an amount sufficient to form a stable particle and to prevent the corrosion of the included iron, but insufficient to decrease the porosity of the activated carbon.
U.S. Pat. No. 3,657,119 to Turbeville discloses that a magnetically susceptible oil-bonding particle may be fabricated from an expandable low density plastic such as polystyrene which has been either impregnated or coated with a plurality of magnetically susceptible particles sufficient to allow the oil-bonding sorbent to be collected by magnetic collection means. Such magnetic collection means are disclosed in the reference as including a buoyant grid having a plurality of parallel spaced ferromagnetic bars which are adapted to collect and contain the oil-sorbent mass. As is disclosed in the Turbeville patent, the sorbent particles may comprise any low density expandable plastic bead which is buoyant and which is also water-resistant.
Following the issuance of the Turbeville patent referred to above, several patents issued each of which disclosed the use of magnetic separation techniques in combination with a magnetically susceptible substance. U.S. Pat. No. 3,803,033 to Sutherland discloses the use of an iron-carbon complex to absorb particulate organic contaminants from a fluid stream and to subsequently remove the complex-contaminant mass by the use of a magnetic filter. U.S. Pat. No. 3,970,518 to Giaever discloses the use of small magnetic particles coated with an antibody layer which antibody layer preferentially attracts specific viruses, bacteria or other cells from a solution containing multicellular, multibacterial or multivirus populations. U.S. Pat. Nos. 3,796,660 and 3,806,449 to kaiser each discloses the use of a "ferrofluid", which ferrofluid comprises a stable colloidal suspension of magnetic particles in a carrier hydrocarbon oil selected from the group consisting of C9-C21 aliphatic hydrocarbons and the saturated C7-C18 napthalenic hydrocarbons and mixtures thereof, for the separation of multiphase liquid-liquid mixtures such as emulsions. In addition to the foregoing, U.S. Pat. Nos. 3,890,224 and 3,923,651 to Weiss disclose a method of removing slicks of oil from aqueous media which comprises firstly treating the oil slick with sufficient fine particles or granules of ferromagnetic material, said granules characterised in that they preferentially absorb or adsorb oil from aqueous media and are buoyant upon the surface of the aqueous media even when associated with oil; and secondly removing the particles, together with associated oil, by magnetic means. The Weiss references disclose that particle sizes of from 500 to 5,000 microns overall diameter are best for such removal operations. The Weiss references further disclose that the ferromagnetic material used for the collection of the oil spill is preferably a synthetic ferromagnetic polymer which is wetable by the oil, and insoluable in both the oil phase and the aqueous phase. Ferromagnetic polymeric materials suitable for use in the invention include polystyrene and copolymers of styrene and polyester, and may include polyesters, methyl methacrylate polymers and copolymers e.g. with ethyleneglycol dimethacrylate, phenol formaldehyde resins, polyvinyl chloride, polyethylene, and polyamides. The ferromagnetic component to be included within the polymer structure is disclosed as being either a soft ferrite, a hard ferrite or material which exhibits reversible magnetism such as gamma-iron oxide, magnetite or chromium dioxide. The Weiss reference also discloses that the oil absorbed or collected onto the ferromagnetic particles or granules may be recovered or removed by physical or chemical means such as washing, pressing, distillation or solvent extraction. Examples included in the Weiss patents disclose the preparation of a co-polymeric styrene and a polyester (see examples 1, 2, 6-9) and of the use of such magnetically susceptible polymeric substrates in the treatment, collection and recovery of oil slicks on the surface of aqueous media (examples, 41 10, 11 and 12). Additional examples (24 and 25) included in the Weiss patent disclose the preparation of vasiculated magnetic polystyrene particles having different particle sizes and porosity and suitable for the removal of oil slicks from water. The results given in these samples indicate that oil pick up efficiency averages approximately 4.5 (weight of oil picked up/weight of particles used.times.100).
In addition to patent references hereinabove cited, significant developmental work has taken place in the private sector directed to the development of suitable hydrocarbon pollutant absorbents for use in the cleaning of pollutant spills. Development of a Polyurethane Foam Marine Oil Recovery System; J. P. Oxinam, R. A. Cochran, B. P. Hemphill and J. P. Fraser; Shell Development Company, Conference Report; presented at the 1973 CONFERENCE ON THE PREVENTION AND CONTROL OF OIL SPILLS, WASHINGTON, D.C. The Oxinam et al. publication disclosed the development of a slab molded polyurethane which may be fabricated at the site of the pollutant spill, which sorbent is effective for the sorption of various hydrocarbon pollutants. Such a polyurethane absorbent, following fabrication on site, may be reduced to suitable sized individual particles and subsequently dispersed upon the surface of the pollutant spill. The sorbent, saturated with pollutant, may subsequently be collected by mechanical collection means.
J. E. Turbeville, in a paper entitled Ferromagnetic Sorbents for Oil Spill Recovery and Control (Environmental Science and Technology, Volume 7, No. 5, 1973, pgs. 433-438) discloses that magnetically susceptible sorbents used in the collection and recovery hydrocarbon pollutants may be collected by a recovery unit including a rotatable drum encircled by a plurality of bands of magnetic material, a wiper blade and a particle-pollutant storage sump. The Turbeville article discloses that magnetically susceptible sorbent particles may be dispersed upon the surface of the pollutant spill, and allowed to form a pollutant-particle mass which tends to retain its integrity on the surface of the aquatic medium. By rotating the drum in the direction of movement of the mass, the particle-pollutant mass will be carried to a point with the magnetic lines of flux of the rotating drum, magnetically bound to the drum and carried thereby out of the water and into contact with the wiping device which is located adjacent the drum surface, which wiping surface removes substantially all of the magnetically bound mass from the drum surface and allows the mass to be collected in the particle-pollutant sump.
Despite the substantial amount of activity directed toward the development of the practical system for the magnetic collection of hydrocarbon pollutant spills, no system appears to have been developed which has enjoyed significant commercial success. Such lack of success in developing a commercially attractive system may be traced to the fact that no presently appearing system appears capable of allowing the efficient handling of the sorbent particles following the hydrocarbon liquid sorbtion and the fact that presently available systems do not appear to efficiently allow the sorbent particles to be recycled in a multi-cycle operation such that a limited amount of sorbent may be continuously recycled to collect and recover a significant amount of hydrocarbon pollutant prior to disposal.
This lack of re-cyclable sorbent appears to be the result of the lack of recognition by those skilled in the art that a non-destructive method of separating the sorbed pollutant from the sorbent is dependent on the utilization of sorbent components which may be freed of pollutant in such a way as to retain the sorptive abilities of the sorbent while refraining from causing detrimental chemical or physical change to the sorbent structure.
It is, of course, immediately apparent that the burning of the pollutant-sorbent mass is suggested by Theiler will not allow sorbent reuse. It is less apparent, by nonetheless true, that the spraying of the pollutant-sorbent mass with chemical agents, such as detergents and the like, as suggested by some of the aforementioned patent references, would introduce water-soluble pollutants into any aquatic medium in which such a "treated" sorbent was introduced for reuse. Thus, if destruction and chemical treatment of the pollutant-sorbent mass are eliminated from consideration as means for the regeneration of a recyclable sorbent, the only immediately apparent remaining alternative is physical separation.
Counted among the available physical methods of separation are filteration, centrifugation, wringing, etc. While each of these methods may accomplish the desired removal of pollutant, filtration and centrifugation are ultimately impractical as each requires equipment of such sophistication and expense that the regenerative process may even be less cost effective than simple destruction. At the same time, the wringing of sorbent particles, while attractive from the economic and efficiency aspects has heretofore been found to be of little utility outside the laboratory due to the fact that the sorbent structure has been found to deteriorate and decompose after a limited number of sorption-wringing cycles.
It is therefore an object of this invention to provide a method and apparatus for the collection and recovery of hydrocarbon pollutant spills.
It is further object of this invention to provide a hydrocarbon pollutant spill collection and recovery system which utilizes magnetic principles.
It is still further object of this invention to provide a magnetic collection and recovery system which allows the efficient recovery of pollutant and separation of the recovered pollutant from the sorbent medium.
It is a still further object of this invention to provide a hydrocarbon pollutant sorbent which may be quickly and efficiently separated from the pollutant by mechanical means for re-use in the pollution recovery process.
It is a still further object of this invention to provide a magnetically susceptible pollution-bonding sorbent.
It is a still further object of this invention to provide a mechanical recovery unit which magnetically collects and recovers a hydrocarbon pollutant saturated absorbent, separates the pollutant from the sorbent, and redistributes the sorbent for further use in the pollutant collecting and recovery operation.